In the second part of our series, Sophia Pathai and Andrew McNaught explain how to approach a patient who has a loss of vision

Being called to see a patient who suddenly complains of loss of vision in one or both eyes can be daunting. Understandably, the patient is often anxious, and you may be as well. The best way to tackle the problem is the same as you would for any other medical problem--start with the history and examination.

History

Find out about the timing of the visual loss--often it happens first thing in the morning--and the onset of symptoms. Did the visual loss last minutes or hours; did the patient wake up with the problem? Beware of "acute" visual loss that is actually of chronic duration but suddenly noticed by the patient; he or she may not be aware of visual loss in one eye until the other eye is occluded--for example, when rubbing an eyelid. Try to establish how severe the visual loss is, it can be just blurring or no perception of light at all. Find out if one or both eyes are affected. It sounds surprising, but patients can mistake a homonymous heminanopia for complete loss of vision in just one eye.

An important distinction to make is the presence or absence of pain; this could be ocular, pain on eye movement, or headache. If the patient does have a headache, then ask about its location; headaches may be temporal or occipital. Also ask about scalp tenderness and jaw claudication as these are all important indicators of temporal arteritis.

Last month, we discussed how a general medical history can give many pointers about an ophthalmic complaint. Make sure that you enquire about any history of cerebrovascular disease, hypertension, and atrial fibrillation as these problems can have ophthalmic complications that can present with loss of vision.

Central retinal artery occlusion

Central retinal vein occlusion

Examination

Try to "fine tune" the examination based on the information obtained from the history. For patients with visual loss, recording acuity accurately and assessing for a relative afferent pupillary defect--as described in last month's article--is essential.¹

The loss of vision may be so profound that Snellen acuity at 6 metres is unrecordable, so you could try measuring from 3 metres. If this does not work, see if the patient can count fingers or detect hand movements. Failing that, record if the patient can perceive light. Test colour vision; obviously a severe visual defect may make this impossible. Testing visual fields with this type of complaint, to exclude a homonymous hemianopia, is essential. A positive relative afferent pupillary defect when examining the pupils is an important finding as it can represent pathology of the retinal or optic nerve.

When performing ophthalmoscopy, remember to look for the red reflex first. Then look at the fundus; is the disc swollen or pale? Does the retina look pale? These suggest ischaemia, as with elsewhere in the body. Is the retina full of haemorrhages and cotton wool spots?

Differential diagnosis

In thinking about the differential diagnosis, we can think about conditions that are relevant to patients with cerebrovascular or cardiovascular disease--those that present with pain and those that are painless.

Related to cerebrovascular or cardiovascular disease

Amaurosis fugax--The patient may describe transient loss of vision in one eye, often described as a curtain coming down over the eye. It may last from seconds to hours, but then normal vision returns. This is because of a temporary interruption to retinal circulation and is usually related to an embolus from the carotid arteries or heart. Results of ophthalmic examinations are often normal. However, a complete cardiovascular examination is essential to look for a potential source of embolus. In particular, assess the pulse for atrial fibrillation, the carotids for bruits, and listen to the heart for murmurs.

Central retinal artery occlusion (CRAO)--The patient may have severe loss of vision needing testing by counting fingers. Often the patient has a relative afferent pupillary defect. The optic disc should look normal; careful examination of the fundus may show the presence of an embolus in a retinal vessel. Blood should be taken for erythrocyte sedimentation rate testing, as central retinal artery occlusion may occur secondary to temporal arteritis.

Branch retinal vein occlusion with flame shaped haemorrhages in the superotemporal region

Central retinal vein occlusion (CRVO)--The visual acuity can be variable, as can the presence of a relative afferent pupillary defect. Generally the ischaemic type of central retinal vein occlusion, which can lead to further ocular complications such as neovascular glaucoma, presents with a more profound loss and a positive relative afferent pupillary defect compared with the non-ischaemic type. Fundoscopy may show flame shaped haemorrhages all over the retina. A branch retinal vein occlusion which affects just one of the peripheral retinal feeder veins is possible but less likely to be associated with severe acute visual loss. Both central retinal vein occlusion and branch retinal vein occlusion can be caused by cardiovascular disease, notably hypertension. In addition, hyperviscosity can also cause this problem and so patients with haematological disorders may be particularly susceptible.

Acute anterior optic ischaemic neuropathy

Anterior ischaemic optic neuropathy (AION)--Infarction of the optic nerve head can occur secondary to an arteritic process such as temporal arteritis (see below), or it may be non-arteritic. The latter is thought to be idiopathic, but can be associated with hypertension, arteriosclerosis, and diabetes. The acuity is reduced and the pupil shows a relative afferent pupillary defect. There may be reduced colour vision and visual fields may show an "altitudinal" field defect or a central scotoma. The optic disc looks swollen, often with haemorrhages on the disc. Temporal arteritis is an important differential diagnosis so taking blood for an erythrocyte sedimentation rate is essential. As the other eye is at risk of developing the same problem, a complete medical evaluation is also needed.

Painless visual loss

Posterior vitreous detachment (PVD) and retinal detachment (RD)--Patients may experience floaters, often described as "cobwebs, spiders, or black blobs." They may also complain of flashing lights. Floaters are common--particularly in shortsighted people--so ascertain if there has been a new onset or change of floaters which may be related to a vitreoretinal problem. Visual loss may follow floaters or flashes which may signal that the retina has detached. Migraine may cause similar symptoms with zigzag flashing lights and temporary visual disturbance. Although posterior vitreous detachments are managed conservatively, patients will need ophthalmic referral to rule out a retinal break in the periphery, or to exclude retinal detachment. You should, however, be able to find out some useful information; the acuity is important as a large decrease in suggests that a retinal detachment may involve the macula. A large detachment may give a positive relative afferent pupillary defect.

Vitreous haemorrhage--A severe haemorrhage may present as sudden loss of vision, sometimes preceded by a storm of red floaters. This may be secondary to medical problems such as diabetes and hypertension, so a full history is necessary. In addition, ask about trauma and drugs, especially aspirin and warfarin. Ophthalmic causes include branch retinal vein occlusion, posterior vitreous detachment or retinal detachment. Examination may show a mild relative afferent pupillary defect, and, on attempting fundoscopy, the red reflex may be absent. Ophthalmic referral is necessary to find the cause of the haemorrhage.

Retinal attachment with prominent folds in the retinal

Loss of vision with pain

Temporal arteritis--As discussed above, infarction of the optic disc may be secondary to an arteritic process. Temporal arteritis affects medium sized arteries of the head and neck. It can, therefore, present as loss of vision because of central retinal artery occlusion or anterior ischaemic optic neuropathy. It may also lead to severe headache, scalp tenderness, and jaw claudication as part of the same inflammatory process. It is closely related to polymyalgia rheumatica, and so patients may give a history of proximal muscle and joint aches. Temporal arteritis is very rare in patients under the age of 50. The patient often has profound visual loss with an associated relative afferent pupillary defect. The disc may look pale and swollen. These signs may also be seen with central retinal artery or vein occlusion, or non-arteritic optic neuropathy, so it's important to have a high index of clinical suspicion in all patients. Take an urgent erythrocyte sedimentation rate; this is often raised, but a normal value does not exclude the diagnosis. Refer urgently to the ophthalmologist. Treatment is with high dose systemic steroids, so it's important to take note of the medical history, particularly diabetes.

Chronic anterior optic ischaemic neuropathy with a pale atrophied disc

Optic neuritis--This has a different age of onset compared with the other conditions, typically affecting 18-45 year olds. The history of visual loss is often subacute, deteriorating over days, although it can occur over hours. The visual loss may be profound or subtle. Patients often complain of pain when moving their eyes and that colours are not as bright as they should be. Test the visual acuity, and test for colour desaturation. A relative afferent pupillary defect will be present if the patient has unilateral optic neuritis. The optic disc may be swollen with flame shaped haemorrhages, or it may look normal. The important differential is a sphenoidal sinusitis, which can present similarly with decreased vision and pain on eye movements. If spotted early on, however, sinus drainage should cure the problem and reverse the optic neuropathy.

Key points

• Make the distinction between painless and painful loss of vision
• Find out about the patient's general medical history
• Cardiovascular and cerebrovascular disease can have ophthalmic manifestations
• Its essential to assess the visual acuity accurately and to examine for a relative afferent pupillary effect
• Keep temporal arteritis at the back of your mind with all losses of vision (whether or not the patient has pain)

Acute closed angle glaucoma--This is an ophthalmology emergency. Beware of a patient who complains of decreased vision and has a red eye. Also watch out for atypical presentations--for example, nausea, vomiting, or abdominal pain--with a seemingly innocuous red eye. We'll go on to discuss this important eye condition in the next article.

Further reading

Elkington AR, Khaw PT. ABC of eyes. 3rd ed. London: BMJ Books, 1999.